Clean up repository before release

[LeonidElkin]

Summary

Cleaned up the repository before the first alpha release preparation.

Changes

• Fixed UNU.RAN CFFI packaging by building vendored sources directly into the extension.
• Added CI checks for package build, metadata validation, clean wheel install, and wheel smoke import.
• Added cibuildwheel configuration for binary wheels.
• Updated package metadata, README, installation docs, and changelog.
• Added Dependabot configuration and SECURITY.md.

Checks

• pre-commit run --all-files
• pytest -q
• python -m build
• twine check
• clean wheel install smoke test

[LeonidElkin]

Why Linux was removed from the cibuildwheel CI job

I initially added cibuildwheel for Linux, macOS, and Windows to validate real wheel builds before release. macOS and Windows wheels build successfully, but the Linux cibuildwheel job currently fails before our package build starts.

The failure happens at the container runtime layer:

docker/podman create ... quay.io/pypa/manylinux2014_x86_64 ... failed